Cutting and coagulating tissue by using a high-frequency current is standard practice in electrosurgery. As is shown in the sectional drawing of FIG. 1, in the so-called monopolar technique, the desired surgical effect is achieved by introducing a HF current into a human or animal body 6 via an active electrode 2, which has a relatively small surface and is supported on a handpiece, and returning it to a HF generator 3 via a neutral electrode 1, which has a relatively large surface and is usually applied to the thigh, sometimes to the upper arm or the back. At the same time, the neutral electrode serves for grounding the patient. Modern neutral electrodes are self-adhesive, single-use contact surfaces of various sizes and shapes.
Unlike an active electrode, where quick heating produces the desired surgical effect, the neutral electrode must not heat the patient's skin by more than 6° C. Corresponding tests are specified in the ANSI-AAMI HF18-93 standard (American National Institute, Association for the Advancement of Medical Instrumentation, Electrosurgical Devices, Arlington, USA, 1993). Here, one electrode type is tested with at least five male and five female subjects under a given current load, and the temperature is usually measured by means of a thermo camera. Alternatively, a substitute medium not described in greater detail, which is demonstrably suited for simulating the electrical and thermal properties of the thermally most sensitive subject, may substitute for the subjects.
Investigation in this field, conducted at the University of Innsbruck, Austria (N. Nessler, H. Huter, L. Wang, Testing Device for Surgical grounding plates, 14′n Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Paris, 1992; H. Huter, Entwicklung eines Meβgerätes für thermische and elektrische Gleichmaβigkeit von Neutraletektroden der HF-Chirurgie, thesis at the University of Innsbruck, 1992; N. Nessler, H. Huter, L. Wang, Sicherheitstester für HF-Chirurgie-Neutralelektroden, Biomedizinische Technik Vol. 38, pp. 5-9, 1993), lead to the development of an electronic device (GPTest 11) which simulates the properties of a patient's skin in a first approximation to such an extent that a neutral electrode can be tested under the current load of 700 mA specified by the AAMI HF18 standard for a measuring time of 60 sec. The temperature increase thus generated is measured and results in measuring values comparable with those obtained with a human subject (N. Nessler, Skin Temperature Scan with Flexible Sensor Array, 16th BEMS Meeting, Copenhagen, 1994; N. Nessler, Current Density Distribution in Human Skin under the Grounding Electrode of Electrosurgery, BEMS 17th Annual Meeting, Boston, Mass., 1995).